/*
 * Copyright 2021 ByteDance Inc.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package caching

import (
	"strings"
	"unsafe"

	"github.com/bytedance/go-tagexpr/v2/binding/gjson/internal/rt"
)

type FieldMap struct {
	N uint64
	b unsafe.Pointer
	m map[string]int
}

type FieldEntry struct {
	ID   int
	Name string
	Hash uint64
}

const (
	FieldMap_N     = int64(unsafe.Offsetof(FieldMap{}.N))
	FieldMap_b     = int64(unsafe.Offsetof(FieldMap{}.b))
	FieldEntrySize = int64(unsafe.Sizeof(FieldEntry{}))
)

func newBucket(n int) unsafe.Pointer {
	v := make([]FieldEntry, n)
	return (*rt.GoSlice)(unsafe.Pointer(&v)).Ptr
}

func CreateFieldMap(n int) *FieldMap {
	return &FieldMap{
		N: uint64(n * 2),
		b: newBucket(n * 2), // LoadFactor = 0.5
		m: make(map[string]int, n*2),
	}
}

func (self *FieldMap) At(p uint64) *FieldEntry {
	off := uintptr(p) * uintptr(FieldEntrySize)
	return (*FieldEntry)(unsafe.Pointer(uintptr(self.b) + off))
}

// Get searches FieldMap by name. JIT generated assembly does NOT call this
// function, rather it implements its own version directly in assembly. So
// we must ensure this function stays in sync with the JIT generated one.
func (self *FieldMap) Get(name string) int {
	h := StrHash(name)
	p := h % self.N
	s := self.At(p)

	/* find the element;
	 * the hash map is never full, so the loop will always terminate */
	for s.Hash != 0 {
		if s.Hash == h && s.Name == name {
			return s.ID
		} else {
			p = (p + 1) % self.N
			s = self.At(p)
		}
	}

	/* not found */
	return -1
}

func (self *FieldMap) Set(name string, i int) {
	h := StrHash(name)
	p := h % self.N
	s := self.At(p)

	/* searching for an empty slot;
	 * the hash map is never full, so the loop will always terminate */
	for s.Hash != 0 {
		p = (p + 1) % self.N
		s = self.At(p)
	}

	/* set the value */
	s.ID = i
	s.Hash = h
	s.Name = name

	/* add the case-insensitive version, prefer the one with smaller field ID */
	key := strings.ToLower(name)
	if v, ok := self.m[key]; !ok || i < v {
		self.m[key] = i
	}
}

func (self *FieldMap) GetCaseInsensitive(name string) int {
	if i, ok := self.m[strings.ToLower(name)]; ok {
		return i
	} else {
		return -1
	}
}
